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The phrase "wave-particle duality" obscures the central mystery in quantum mechanics. You can visualize waves quantized into particles - that's not mysterious.

The phrase "wave-particle duality" obscures the central mystery in quantum mechanics. You can visualize waves quantized into particles - that's not mysterious. But how does a single particle create an interference pattern when there's no other particles for it to interfere with? And how does covering up one slit destroy the interference pattern when there is only one particle going though one of the slits in the first place? Just saying "wave-particle duality explains it" is false. It was a shock for me to realize that everything taught in physics textbooks was so misleading. (For a good explanation see MWI)

katmannthree 7y ago
Unfortunately in my experience people aren't fond of the more correct explanation, which is that entities on the atomic scale don't behave in ways directly analogous to anything humans are intuitively familiar with.
- pasquinelli 7y ago
  People aren't fond of that explanation because it isn't an explanation. "Why do some stars make loop-de-loops as they traverse the sky?" "Because entities on the celestial scale don't behave in ways directly analogous to anything humans are intuitively familiar with." "Oh..."
  - juped 7y ago
    Well... they don't, unless those humans are differential geometers.
    - RangerScience 7y ago
      ....Or play enough KSP.
      - juped 7y ago
        KSP doesn't simulate GR
        RangerScience 7y ago
        :crosses fingers for KSP 2: Sure. But, AFAIK, newtonian physics covers most of the behavior of the planets; that GR affects the timing rather than the paths. Or am I substantially wrong?
  - katmannthree 7y ago
    Does it not strike you as a rather peculiar viewpoint that everything that exists should be easily understandable by untrained humans? That's quite a thing to expect from the universe. It's not just "not an explanation", it's declaring that there _is no_ correct and easily understandable mathfree explanation or analogy. The only way you can properly understand things like this is within the context of the experimental measurements we've made and the mathematical models we've developed as a result. There's no way to explain these to a five year old in a way that's not significantly incorrect (unless perhaps they happen to be uncommonly good at linear algebra) . The current layperson explanation is so significantly incorrect that I think it's actually detrimental. Photons aren't "particles" like marbles, and they're not also "waves" like you see on the ocean. They're sure as hell not both at the same time in some sort of religiously inspired "don't question it" union. What they are are entities, abstract things that we can create and play with and measure. We can make somewhat complicated mathematical models to predict certain aspects of their (and similar entity's) behavior. They at times exhibit behavior one would expect from a particle. In other cases they exhibit behavior one would expect from a wave. They're neither though, they're their own thing that behave by their own rules. That's it.
    - RangerScience 7y ago
      Don't forget, kiddos! You're made of star stuff ...and that star stuff is made of math... and that math is not just any math, it's probability math.
  - 2zcon 7y ago
    But we're not intuitively familiar with what happens when those stars get really big and start being black holes and exhibiting relativity. Fortunately, like waves, we can manage the maths.
  - Erlich_Bachman 7y ago
    > People aren't fond of that explanation because it isn't an explanation. It absolutely is an explanation. The explanation is not just "they don't behave as neutonian macro objects" - that's the a beginning of it. The explanation itself comes after when physicists describe in exact ways how these quantum objects behave, explained so specifically that it can be calculated upon with specific equations. The fact that those explanations don't fit in your current set of intuitions about world and objects in it is more of a "you-problem", not "physics-problem". The universe has no obligation to make sense to you, it is more of your job to create those new intuitions in your mind and those new models of the world. While the physicists have provided you with all the needed tools, it is still up to you to build them into your mind.
    - brutt 7y ago
      Quantum physics can be explained in single picture. I did it (in Ukrainian): https://www.facebook.com/groups/194031297610629/permalink/1030959753917775/ https://www.facebook.com/groups/194031297610629/permalink/10... . It's easy to explain.
      - zentiggr 7y ago
        Any way to see that from a non-FB URL?
        brutt 7y ago
        It awfully simple. I took screenshot from this video: https://www.youtube.com/watch?v=nsaUX48t0w8 https://www.youtube.com/watch?v=nsaUX48t0w8 , then label things: particle, wave, interference, and quanta. Nothing special at all.
mbell 7y ago
> But how does a single particle create an interference pattern when there's no other particles for it to interfere with? The particles aren't interfering with each other. A wave is interfering with itself due to the two slits 'splitting' the wave. The presence of other particles has no baring on this. > And how does covering up one slit destroy the interference pattern when there is only one particle going though one of the slits in the first place? With one slit you don't split the wave so there is no interference. The particle doesn't go through one of the slits, it goes through both simultaneously in 'wave form', this is the mystery.
- ridewinter 7y ago
  Place a detector in front of the slits. Only a single particle in a single slit is detected. There is no "splitting" of the particle that we can see. Edit: If you try to actually define "wave function collapse" and "observer" you are back into the same mumbo-jumbo as "wave-particle duality". They are just placeholders that obscure the mystery.
  - richardw 7y ago
    We know it arrives as a particle. We don’t know it travels as a particle. What we know is that it acts very wave-like when it travels. If I were forced to bet, I’d say it travels like a wave and arrives like a particle. That doesn’t mean “duality”. It means the condition required to arrive somewhere require a set of values that are packet-like. But we insist that it’s a packet all the way through, so the discussion remains confusing to lay people for 100 years. If you measure before/at the slit you affect the experiment. You affect how it travels through the slits, removing the interference pattern. So yes it’s not split but that has no bearing on when the detector is not at the slit. They’re different situations and have different outcomes.
    - imtringued 7y ago
      So you are saying that light is always a wave but when it is being absorbed by an atom it somehow consumes the "entire" wave, no matter how spread out?
BoiledCabbage 7y ago
Isn't a better and "simpler" explanation, Pilot wave theory? Particles are like boats on a lake - they both cause waves when they move and are moved by relfections of their own and other boats' wakes. Interference is simply waves generated by a boat interfering with other waves from the boat.
- btmorex 7y ago
  Unless your boat can simultaneously pass through two different arches of the same bridge, I don't really think that helps.
  - jayd16 7y ago
    The wave a boat makes can certainly travel through two arches in a bridge.
  - brutt 7y ago
    Boat cannot, but wave can. https://www.youtube.com/watch?v=nsaUX48t0w8 https://www.youtube.com/watch?v=nsaUX48t0w8
- aeternum 7y ago
  Pilot wave theory isn't actually simpler because the pilot wave must travel throughout the entire universe instantaneously. According to the theory, classical information cannot be sent along the wave so it does not violate no-communication, however the prospect of having a wave that travels instantaneously and permeates the entire universe is still hard for many to accept.
  - eagsalazar2 7y ago
    Does it require that? Can you elaborate? I haven't heard of this issue with Pilot Wave Theory before.
    - aeternum 7y ago
      It's not just an issue with Pilot Wave, many QM interpretations are non-local. This table shows which are vs. are not (Local Dynamics column): https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics https://en.wikipedia.org/wiki/Interpretations_of_quantum_mec...
ars 7y ago
MWI doesn't explain much. Why should this electron be able to cross universes and talk to another one and interfere, while nothing else can cross universes? Can I setup my experiment so that quantum decay decides if I emit an electron or not - and then wait for no electron, but I somehow detect the electron that was released in a another universe? MWI also doesn't explain why the individual electrons would take different paths and interfere with each other - the universes are identical, so why are the electrons taking different paths?
- ridewinter 7y ago
  Why should this electron be able to cross universes and talk to another one and interfere, while nothing else can cross universes? See "decoherence": https://en.m.wikipedia.org/wiki/Quantum_decoherence https://en.m.wikipedia.org/wiki/Quantum_decoherence
- jiggawatts 7y ago
  > cross universes? MWI is a local theory. Changes spread out at the speed of light, they just spread out (and back from) adjacent universes as well. https://www.hedweb.com/manworld.htm#local https://www.hedweb.com/manworld.htm#local > the universes are identical... Think of a 3D volume of space with a plane wave travelling through it, such as a beam of coherent laser light. An alternative way of thinking about this is that each point emits a spherical wave and the plane wave is just constructive interference of a continuum of spherical waves. In many worlds theories, you can think of each point as also spreading out into non-spatial dimensions that are directions towards other universes. Similarly, aggregate behaviour is the constructive interference of not just the points in "one" universe, but also the points in a neighbouring "volume" of universes. If the neighbouring universes are identical, or nearly so, it's like the coherent laser scenario. If they're all different, it's more like white light -- it's unpredictable and "random", but otherwise it's still just ordinary light. Very slight deviations would result in various interference effects, such as the double-slit scenario.
- kanzenryu2 7y ago
  These are exactly the sort of thing MWI precisely explains. It take time to go through, but this is the best explanation I've ever seen https://www.lesswrong.com/posts/apbcLXz5zB7PXfgg2/an-intuitive-explanation-of-quantum-mechanics https://www.lesswrong.com/posts/apbcLXz5zB7PXfgg2/an-intuiti...
lawrenceyan 7y ago
Particles don't really exist. Nor do waves for that matter either. Generally these days, it's considered more correct to think in terms of fields and excitations. Even then though it's important to realize that what we're working with are models. Very powerful and extremely accurate models, but still models nonetheless at the end of the day.
- ridewinter 7y ago
  Yes, true. The particle is a quantized excitation of the field that travels in a wave. The original point remains.
magicalhippo 7y ago
Earlier this week I had an idle thought around the measurement problem, did some searching when I came home and stumbled over this[1] paper where they show that the degree of "waveiness" V and degree of "particleness" P of a particle is related to the degree of self-entanglement C: V^2 + P^2 + C^2 = 1 They've since done a follow-up experiment[2] to demonstrate it in a quantum setup as well (first paper did classical experiment). I'm just a layman so have no idea how profound this is, but I found it interesting. [1]: https://www.osapublishing.org/optica/abstract.cfm?uri=optica-5-8-942 https://www.osapublishing.org/optica/abstract.cfm?uri=optica... (open access) [2]: https://arxiv.org/abs/2001.01749 https://arxiv.org/abs/2001.01749
- RangerScience 7y ago
  What. So cool. Thank you!
wilg 7y ago
I highly recommend PBS Digital's Space Time for a great overview (and deeper mathy dives) into modern physics: https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g There are lots of videos about the various interpretations of quantum weirdness through a robust scientific lens, while still being entertaining enough to watch even if you don't grasp all the details.
tsimionescu 7y ago
Interestingly, there is a (possibly still incomplete?) model of QM that explains this mystery and can even be replicated in human scale experiments: The de Broglie-Bohm pilot wave model. In this model, both the wave and the particle are simultaneously real. the particle is being moved around by the wave. When we get near the double slit, the wave naturally travels through both slits and forms an interference pattern.The particle randomly moves through one of the slits, and is them carried further by the interference pattern, the highest probability being that it will be carried to one of the local maxima. The nicest part is that this exact behavior can be seen by bouncing a droplet of oil or silicone on a vibrating bath of the same material: https://www.youtube.com/watch?v=nsaUX48t0w8 https://www.youtube.com/watch?v=nsaUX48t0w8 . Of course, this being a consistent model for QM, it doesn't get away from the Bell inequalities, it doesn't have local realism. It does preserve realism, but it it is a nonlocal theory (some effects travel instantaneously).
- brutt 7y ago
  Moreover, we can label things in this experiment, because we see cause and effect. We can clearly label particle (droplet), wave (around droplet), interference caused by wave with itself (when it goes trough both slits), and quanta (single wave, distance between two valleys).
tagh 7y ago
Of course there is no proven interpretation, but I quite like MWI. From my understanding of the theory, the particle does not interfere with itself: the particle follows all possible trajectories in each different 'world', and we observe but one of those trajectories. Once multiple particles are fired, we are _overwhelmingly_ likely to observe a wave-like detection pattern. One poor universe, however, sees no evidence of wave-like behaviour at all!
- RangerScience 7y ago
  IMHO it's weirder than that. Here's my bad explanation of a theory, and uneducated interpretation There's a paper out there about positing a series of non-quantum universes (particles that aren't also waves), except where each universe exerts a force on all other universes to not be identical. Apparently, under this framework, for N such universes you get an N-step approximation of the wave form (reaching the wave form as n->infinity). Which is pretty cool in an of itself, _and then_... We observe the wave form. Does that then mean we're observing across all of those universes?
eagsalazar2 7y ago
Pilot wave theory is simplest and most obvious interpretation IMO. We already accept the Higgs field that permeates all space-time (and predictions of that theory were verified by discovery of Higgs Boson) so why can't there be waves in that or another omnipresent medium that these particles are "riding" on? These double slit, wave-particle dualities, and all the other bizarre notions (apart from non-locality which both predict) vanish with the pilot wave theory. Never understood why Copenhagen interpretation has so much mindshare except it's more sensational, controversial nature and the personalities that advocated for it.
irthomasthomas 7y ago
This reminds me of something I read about the time invariance in QED. I forgets the details, but I think it was Feynman who said that when you learn QM, you learn about these equations which are time invariant, they produce symeytical equations where the left side is a particle is travelling backwards in time, and the right side is travelling forwards in time. And your professor waves his hands and says we'll deal with that later. Then eventually at the end of your studies you just wipe the left side off the board and ignore it.
dcow 7y ago
I’m fond of the deterministic Bohmian interpretation myself: https://en.wikipedia.org/wiki/Pilot_wave_theory https://en.wikipedia.org/wiki/Pilot_wave_theory. And there’s nothing particularly obscure about it...
- fsh 7y ago
  Bohmian mechanics is very obscure. It is explicitly non-relativistic (unlike the universe we live in), and sometimes predics very weird trajectories: https://www.degruyter.com/view/j/zna.1992.47.issue-12/zna-1992-1201/zna-1992-1201.xml?lang=en https://www.degruyter.com/view/j/zna.1992.47.issue-12/zna-19... There is a reason why almost nobody is taking it seriously.
  - BoiledCabbage 7y ago
    You link to a paper (ESSW) that walked through a theoretical experiment that they claimed would show it as being non-relativistic, the paper actually argues it was "surrealistic", not "non-relativistic". That said they don't actually perform the experiment, they just claim it would falsify things. They don't get to claim something is false because they think it would happen if they did the experiment. Actually do the experiment and see what happens. > A real experiment along these lines appears feasible, as all components of the apparatus have been realized separately; for details consult Appendix A. The purpose of the proposed experiment is to verify the predicted quantum theoretical correlations: Whenever an atom hits the screen in the lower region A, the upper detector says "yes" - and likewise for the upper region B and the lower detector. Since we know that (some of) the retrodicted Böhm trajectories pass through the other detector, this verification suffices to demonstrate the asserted metaphysical character of the Böhm trajectories. Now all of that said, a group actually did the experiment and showed that they only way someone would incorrectly conclude the trajectories were surrealistic would be if they mistakenly ignored the non-local nature of their behavior. They actually performed an experiment and demonstrated the results. https://advances.sciencemag.org/content/2/2/e1501466.full https://advances.sciencemag.org/content/2/2/e1501466.full > We have verified the effect pointed out by ESSW that for a WWM with a delayed readout, Bohmian trajectories originating at the lower slit may be accompanied by WWM results associated with either the upper or the lower slit. However, this surreal behavior is merely the flip side of the nonlocality we also demonstrated. In Fig. 3, we showed that the trajectory of photon 1 depends on the choice of measurement (polarization basis) for photon 2. In Fig. 4, we see that the polarization of photon 2 depends on the choice of when (that is, at what point along the trajectory) to measure the position of photon 1. This nonlocality is due to the entanglement of the two photons, which, in Bohmian mechanics, makes their evolution inseparable even when the photons themselves are separated. Because entanglement is necessary for the delayed measurement scenario of ESSW, this nonlocal behavior is to be expected and is the reason for the surreal behavior they identify. Indeed, our observation of the change in polarization of a free space photon, as a function of the time of measurement of a distant photon (along one reconstructed trajectory), is an exceptionally compelling visualization of the nonlocality inherent in any realistic interpretation of quantum mechanics. Essentially the claim in the paper you linked was incorrect, and experimentally demonstrated to be so.
nathias 7y ago
that a particle behaves at the same time as a wave and a particle is the mystery

katmannthree 7y ago

Unfortunately in my experience people aren't fond of the more correct explanation, which is that entities on the atomic scale don't behave in ways directly analogous to anything humans are intuitively familiar with.

pasquinelli 7y ago
People aren't fond of that explanation because it isn't an explanation. "Why do some stars make loop-de-loops as they traverse the sky?" "Because entities on the celestial scale don't behave in ways directly analogous to anything humans are intuitively familiar with." "Oh..."
- juped 7y ago
  Well... they don't, unless those humans are differential geometers.
  - RangerScience 7y ago
    ....Or play enough KSP.
    - juped 7y ago
      KSP doesn't simulate GR
      - RangerScience 7y ago
        :crosses fingers for KSP 2: Sure. But, AFAIK, newtonian physics covers most of the behavior of the planets; that GR affects the timing rather than the paths. Or am I substantially wrong?
- katmannthree 7y ago
  Does it not strike you as a rather peculiar viewpoint that everything that exists should be easily understandable by untrained humans? That's quite a thing to expect from the universe. It's not just "not an explanation", it's declaring that there _is no_ correct and easily understandable mathfree explanation or analogy. The only way you can properly understand things like this is within the context of the experimental measurements we've made and the mathematical models we've developed as a result. There's no way to explain these to a five year old in a way that's not significantly incorrect (unless perhaps they happen to be uncommonly good at linear algebra) . The current layperson explanation is so significantly incorrect that I think it's actually detrimental. Photons aren't "particles" like marbles, and they're not also "waves" like you see on the ocean. They're sure as hell not both at the same time in some sort of religiously inspired "don't question it" union. What they are are entities, abstract things that we can create and play with and measure. We can make somewhat complicated mathematical models to predict certain aspects of their (and similar entity's) behavior. They at times exhibit behavior one would expect from a particle. In other cases they exhibit behavior one would expect from a wave. They're neither though, they're their own thing that behave by their own rules. That's it.
  - RangerScience 7y ago
    Don't forget, kiddos! You're made of star stuff ...and that star stuff is made of math... and that math is not just any math, it's probability math.
- 2zcon 7y ago
  But we're not intuitively familiar with what happens when those stars get really big and start being black holes and exhibiting relativity. Fortunately, like waves, we can manage the maths.
- Erlich_Bachman 7y ago
  > People aren't fond of that explanation because it isn't an explanation. It absolutely is an explanation. The explanation is not just "they don't behave as neutonian macro objects" - that's the a beginning of it. The explanation itself comes after when physicists describe in exact ways how these quantum objects behave, explained so specifically that it can be calculated upon with specific equations. The fact that those explanations don't fit in your current set of intuitions about world and objects in it is more of a "you-problem", not "physics-problem". The universe has no obligation to make sense to you, it is more of your job to create those new intuitions in your mind and those new models of the world. While the physicists have provided you with all the needed tools, it is still up to you to build them into your mind.
  - brutt 7y ago
    Quantum physics can be explained in single picture. I did it (in Ukrainian): https://www.facebook.com/groups/194031297610629/permalink/1030959753917775/ https://www.facebook.com/groups/194031297610629/permalink/10... . It's easy to explain.
    - zentiggr 7y ago
      Any way to see that from a non-FB URL?
      - brutt 7y ago
        It awfully simple. I took screenshot from this video: https://www.youtube.com/watch?v=nsaUX48t0w8 https://www.youtube.com/watch?v=nsaUX48t0w8 , then label things: particle, wave, interference, and quanta. Nothing special at all.

mbell 7y ago

> But how does a single particle create an interference pattern when there's no other particles for it to interfere with? The particles aren't interfering with each other. A wave is interfering with itself due to the two slits 'splitting' the wave. The presence of other particles has no baring on this. > And how does covering up one slit destroy the interference pattern when there is only one particle going though one of the slits in the first place? With one slit you don't split the wave so there is no interference. The particle doesn't go through one of the slits, it goes through both simultaneously in 'wave form', this is the mystery.

ridewinter 7y ago
Place a detector in front of the slits. Only a single particle in a single slit is detected. There is no "splitting" of the particle that we can see. Edit: If you try to actually define "wave function collapse" and "observer" you are back into the same mumbo-jumbo as "wave-particle duality". They are just placeholders that obscure the mystery.
- richardw 7y ago
  We know it arrives as a particle. We don’t know it travels as a particle. What we know is that it acts very wave-like when it travels. If I were forced to bet, I’d say it travels like a wave and arrives like a particle. That doesn’t mean “duality”. It means the condition required to arrive somewhere require a set of values that are packet-like. But we insist that it’s a packet all the way through, so the discussion remains confusing to lay people for 100 years. If you measure before/at the slit you affect the experiment. You affect how it travels through the slits, removing the interference pattern. So yes it’s not split but that has no bearing on when the detector is not at the slit. They’re different situations and have different outcomes.
  - imtringued 7y ago
    So you are saying that light is always a wave but when it is being absorbed by an atom it somehow consumes the "entire" wave, no matter how spread out?

BoiledCabbage 7y ago

Isn't a better and "simpler" explanation, Pilot wave theory? Particles are like boats on a lake - they both cause waves when they move and are moved by relfections of their own and other boats' wakes. Interference is simply waves generated by a boat interfering with other waves from the boat.

btmorex 7y ago
Unless your boat can simultaneously pass through two different arches of the same bridge, I don't really think that helps.
- jayd16 7y ago
  The wave a boat makes can certainly travel through two arches in a bridge.
- brutt 7y ago
  Boat cannot, but wave can. https://www.youtube.com/watch?v=nsaUX48t0w8 https://www.youtube.com/watch?v=nsaUX48t0w8
aeternum 7y ago
Pilot wave theory isn't actually simpler because the pilot wave must travel throughout the entire universe instantaneously. According to the theory, classical information cannot be sent along the wave so it does not violate no-communication, however the prospect of having a wave that travels instantaneously and permeates the entire universe is still hard for many to accept.
- eagsalazar2 7y ago
  Does it require that? Can you elaborate? I haven't heard of this issue with Pilot Wave Theory before.
  - aeternum 7y ago
    It's not just an issue with Pilot Wave, many QM interpretations are non-local. This table shows which are vs. are not (Local Dynamics column): https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics https://en.wikipedia.org/wiki/Interpretations_of_quantum_mec...

ars 7y ago

MWI doesn't explain much. Why should this electron be able to cross universes and talk to another one and interfere, while nothing else can cross universes? Can I setup my experiment so that quantum decay decides if I emit an electron or not - and then wait for no electron, but I somehow detect the electron that was released in a another universe? MWI also doesn't explain why the individual electrons would take different paths and interfere with each other - the universes are identical, so why are the electrons taking different paths?

ridewinter 7y ago
Why should this electron be able to cross universes and talk to another one and interfere, while nothing else can cross universes? See "decoherence": https://en.m.wikipedia.org/wiki/Quantum_decoherence https://en.m.wikipedia.org/wiki/Quantum_decoherence
jiggawatts 7y ago
> cross universes? MWI is a local theory. Changes spread out at the speed of light, they just spread out (and back from) adjacent universes as well. https://www.hedweb.com/manworld.htm#local https://www.hedweb.com/manworld.htm#local > the universes are identical... Think of a 3D volume of space with a plane wave travelling through it, such as a beam of coherent laser light. An alternative way of thinking about this is that each point emits a spherical wave and the plane wave is just constructive interference of a continuum of spherical waves. In many worlds theories, you can think of each point as also spreading out into non-spatial dimensions that are directions towards other universes. Similarly, aggregate behaviour is the constructive interference of not just the points in "one" universe, but also the points in a neighbouring "volume" of universes. If the neighbouring universes are identical, or nearly so, it's like the coherent laser scenario. If they're all different, it's more like white light -- it's unpredictable and "random", but otherwise it's still just ordinary light. Very slight deviations would result in various interference effects, such as the double-slit scenario.
kanzenryu2 7y ago
These are exactly the sort of thing MWI precisely explains. It take time to go through, but this is the best explanation I've ever seen https://www.lesswrong.com/posts/apbcLXz5zB7PXfgg2/an-intuitive-explanation-of-quantum-mechanics https://www.lesswrong.com/posts/apbcLXz5zB7PXfgg2/an-intuiti...

lawrenceyan 7y ago

Particles don't really exist. Nor do waves for that matter either. Generally these days, it's considered more correct to think in terms of fields and excitations. Even then though it's important to realize that what we're working with are models. Very powerful and extremely accurate models, but still models nonetheless at the end of the day.

ridewinter 7y ago
Yes, true. The particle is a quantized excitation of the field that travels in a wave. The original point remains.

magicalhippo 7y ago

Earlier this week I had an idle thought around the measurement problem, did some searching when I came home and stumbled over this[1] paper where they show that the degree of "waveiness" V and degree of "particleness" P of a particle is related to the degree of self-entanglement C: V^2 + P^2 + C^2 = 1 They've since done a follow-up experiment[2] to demonstrate it in a quantum setup as well (first paper did classical experiment). I'm just a layman so have no idea how profound this is, but I found it interesting. [1]: https://www.osapublishing.org/optica/abstract.cfm?uri=optica-5-8-942 https://www.osapublishing.org/optica/abstract.cfm?uri=optica... (open access) [2]: https://arxiv.org/abs/2001.01749 https://arxiv.org/abs/2001.01749

RangerScience 7y ago
What. So cool. Thank you!

wilg 7y ago

I highly recommend PBS Digital's Space Time for a great overview (and deeper mathy dives) into modern physics: https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g There are lots of videos about the various interpretations of quantum weirdness through a robust scientific lens, while still being entertaining enough to watch even if you don't grasp all the details.

tsimionescu 7y ago

Interestingly, there is a (possibly still incomplete?) model of QM that explains this mystery and can even be replicated in human scale experiments: The de Broglie-Bohm pilot wave model. In this model, both the wave and the particle are simultaneously real. the particle is being moved around by the wave. When we get near the double slit, the wave naturally travels through both slits and forms an interference pattern.The particle randomly moves through one of the slits, and is them carried further by the interference pattern, the highest probability being that it will be carried to one of the local maxima. The nicest part is that this exact behavior can be seen by bouncing a droplet of oil or silicone on a vibrating bath of the same material: https://www.youtube.com/watch?v=nsaUX48t0w8 https://www.youtube.com/watch?v=nsaUX48t0w8 . Of course, this being a consistent model for QM, it doesn't get away from the Bell inequalities, it doesn't have local realism. It does preserve realism, but it it is a nonlocal theory (some effects travel instantaneously).

brutt 7y ago
Moreover, we can label things in this experiment, because we see cause and effect. We can clearly label particle (droplet), wave (around droplet), interference caused by wave with itself (when it goes trough both slits), and quanta (single wave, distance between two valleys).

tagh 7y ago

Of course there is no proven interpretation, but I quite like MWI. From my understanding of the theory, the particle does not interfere with itself: the particle follows all possible trajectories in each different 'world', and we observe but one of those trajectories. Once multiple particles are fired, we are _overwhelmingly_ likely to observe a wave-like detection pattern. One poor universe, however, sees no evidence of wave-like behaviour at all!

RangerScience 7y ago
IMHO it's weirder than that. Here's my bad explanation of a theory, and uneducated interpretation There's a paper out there about positing a series of non-quantum universes (particles that aren't also waves), except where each universe exerts a force on all other universes to not be identical. Apparently, under this framework, for N such universes you get an N-step approximation of the wave form (reaching the wave form as n->infinity). Which is pretty cool in an of itself, _and then_... We observe the wave form. Does that then mean we're observing across all of those universes?

eagsalazar2 7y ago

Pilot wave theory is simplest and most obvious interpretation IMO. We already accept the Higgs field that permeates all space-time (and predictions of that theory were verified by discovery of Higgs Boson) so why can't there be waves in that or another omnipresent medium that these particles are "riding" on? These double slit, wave-particle dualities, and all the other bizarre notions (apart from non-locality which both predict) vanish with the pilot wave theory. Never understood why Copenhagen interpretation has so much mindshare except it's more sensational, controversial nature and the personalities that advocated for it.

irthomasthomas 7y ago

This reminds me of something I read about the time invariance in QED. I forgets the details, but I think it was Feynman who said that when you learn QM, you learn about these equations which are time invariant, they produce symeytical equations where the left side is a particle is travelling backwards in time, and the right side is travelling forwards in time. And your professor waves his hands and says we'll deal with that later. Then eventually at the end of your studies you just wipe the left side off the board and ignore it.

dcow 7y ago

I’m fond of the deterministic Bohmian interpretation myself: https://en.wikipedia.org/wiki/Pilot_wave_theory https://en.wikipedia.org/wiki/Pilot_wave_theory. And there’s nothing particularly obscure about it...

fsh 7y ago
Bohmian mechanics is very obscure. It is explicitly non-relativistic (unlike the universe we live in), and sometimes predics very weird trajectories: https://www.degruyter.com/view/j/zna.1992.47.issue-12/zna-1992-1201/zna-1992-1201.xml?lang=en https://www.degruyter.com/view/j/zna.1992.47.issue-12/zna-19... There is a reason why almost nobody is taking it seriously.
- BoiledCabbage 7y ago
  You link to a paper (ESSW) that walked through a theoretical experiment that they claimed would show it as being non-relativistic, the paper actually argues it was "surrealistic", not "non-relativistic". That said they don't actually perform the experiment, they just claim it would falsify things. They don't get to claim something is false because they think it would happen if they did the experiment. Actually do the experiment and see what happens. > A real experiment along these lines appears feasible, as all components of the apparatus have been realized separately; for details consult Appendix A. The purpose of the proposed experiment is to verify the predicted quantum theoretical correlations: Whenever an atom hits the screen in the lower region A, the upper detector says "yes" - and likewise for the upper region B and the lower detector. Since we know that (some of) the retrodicted Böhm trajectories pass through the other detector, this verification suffices to demonstrate the asserted metaphysical character of the Böhm trajectories. Now all of that said, a group actually did the experiment and showed that they only way someone would incorrectly conclude the trajectories were surrealistic would be if they mistakenly ignored the non-local nature of their behavior. They actually performed an experiment and demonstrated the results. https://advances.sciencemag.org/content/2/2/e1501466.full https://advances.sciencemag.org/content/2/2/e1501466.full > We have verified the effect pointed out by ESSW that for a WWM with a delayed readout, Bohmian trajectories originating at the lower slit may be accompanied by WWM results associated with either the upper or the lower slit. However, this surreal behavior is merely the flip side of the nonlocality we also demonstrated. In Fig. 3, we showed that the trajectory of photon 1 depends on the choice of measurement (polarization basis) for photon 2. In Fig. 4, we see that the polarization of photon 2 depends on the choice of when (that is, at what point along the trajectory) to measure the position of photon 1. This nonlocality is due to the entanglement of the two photons, which, in Bohmian mechanics, makes their evolution inseparable even when the photons themselves are separated. Because entanglement is necessary for the delayed measurement scenario of ESSW, this nonlocal behavior is to be expected and is the reason for the surreal behavior they identify. Indeed, our observation of the change in polarization of a free space photon, as a function of the time of measurement of a distant photon (along one reconstructed trajectory), is an exceptionally compelling visualization of the nonlocality inherent in any realistic interpretation of quantum mechanics. Essentially the claim in the paper you linked was incorrect, and experimentally demonstrated to be so.

nathias 7y ago

that a particle behaves at the same time as a wave and a particle is the mystery